The invention relates to pump assemblies.
The invention relates to a pump assembly of the kind comprising an inlet, an outlet and a pump housing having an inlet aperture in fluid connection with the inlet and an outlet aperture in fluid connection with the outlet, a rotor within the housing and shaped to form with an interior surface of the housing at least one chamber that on rotation of the rotor conveys fluid from the inlet aperture to the outlet aperture, the housing carrying a seal between the inlet and the outlet and located in the inlet and urged into contact with the rotor to prevent the passage of fluid past the rotor from the outlet to the inlet. Such pump assemblies are known from, for example, WO2006/027548 and WO2010/12229.
The location of the inlet aperture and the outlet aperture affects the performance of the pump. The operation of the pump is optimised if respective circumferential edges of the inlet aperture and the outlet aperture have respective portions that are closely adjacent (including at) respective circumferential edges of the seal. If these portions are spaced from these edges, it can create negative pressures locally as the rotor rotates. In addition, the inlet and the outlet apertures, in planes normal to the rotor axis and where they enter to housing, generally extend all or mainly to one side of a diameter of the housing that includes the seal and is normal to a radius of the housing passing through the line of contact of the seal with the rotor (“the contact radius”) so that a second portion of the circumferential edge opposite the first portion is spaced further from the contact radius than the first portion.
Where the pump assembly is used to draw fluid from a container, it is advantageous for the inlet and the outlet to open in opposite directions and to be shaped to have respective centre lines that lie in a plane normal to the axis of the rotor. Often, the centre lines will be parallel. This allows the inlet to be a push fit onto an under surface of a container for the supply of fluid to an open end of the inlet and allows the fluid to be dispensed downwardly from an open end of the outlet. Such a pump assembly can be formed by moulding in a process that uses mould tools including cores to form the housing including the seal, the inlet and the outlet and the inlet and outlet apertures.
Where the contact radius is parallel to the centre lines of the inlet and the outlet, the direction of opening of the inlet aperture is towards the open end of the inlet and so the inlet aperture can be formed by moving a simple one-piece first core in a linear movement until a face of the first core abuts a face of a second core forming the interior of the housing and then retracting the first core along the same line. In this case, however, the direction of opening of the outlet aperture is also towards the open end of the inlet and so is away from the open end of the outlet. This prevents the outlet aperture being formed by moving a simple one-piece third core in a linear movement until a face of the third core abuts a face of the second core and by retracting the third core along the same line. It is necessary to use a complicated single core or a number of cores as seen, for example, in PCT/EP2012/069643. This increases the complexity of manufacture and the cost of the pump assembly.